Catégorie : Collaborations

Abstract : We consider the electronic transport in multi-terminal mesoscopic networks of weakly disordered metallic wires. After a brief description of the classical transport, we analyze the weak localisation (WL) correction to the four-terminal resistances, which involves an integration of the Cooperon over the wires with proper weights. We provide an interpretation of these weights in terms of classical transport properties. We illustrate the formalism on examples and show that weak localisation to four-terminal conductances may become large in some situations. In a second part, we study the correlations of four-terminal resistances and show that integration of Diffuson and Cooperon inside the network involves the same weights as the WL. The formulae are applied to multiconnected wire geometries.

1 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
2 LPS – Laboratoire de Physique des Solides

Richard Legras 1 David Rio 2
1 LuMIn – Laboratoire Lumière, Matière et Interfaces
2 LAC – Laboratoire Aimé Cotton

Guillaume Vandermeer David Rio 1 Jean-Jacques Gicquel Pierre-Jean Pisella 2 Richard Legras 3
1 LAC – Laboratoire Aimé Cotton
2 Université Francois Rabelais [Tours]
3 LuMIn – Laboratoire Lumière, Matière et Interfaces

A. Tallaire 1 M. Lesik 2 V. Jacques 3 S. Pezzagna 4 V. Mille 1 O. Brinza 1 J. Meijer 4 B. Abel J.F. Roch 2 A. Gicquel 1 J. Achard 1
1 LSPM – Laboratoire des Sciences des Procédés et des Matériaux
2 LAC – Laboratoire Aimé Cotton
3 LPS – Laboratoire de Physique des Solides
4 Universität Leipzig [Leipzig]

M. Lesik 1 T. Plays 1 A. Tallaire 2 J. Achard 2 O. Brinza 2 L. William 2 M. Chipaux 3 L. Toraille 1 T. Debuisschert 3 A. Gicquel 2 J.F. Roch 1 V. Jacques 4
1 LAC – Laboratoire Aimé Cotton
2 LSPM – Laboratoire des Sciences des Procédés et des Matériaux
3 TRT – Thales Research and Technologies [Orsay]
4 LPS – Laboratoire de Physique des Solides

Abstract : The capacity to propagate magnetic domain walls with spin-polarized currents underpins several schemes for information storage and processing using spintronic devices. A key question involves the internal structure of the domain walls, which governs their response to certain current-driven torques such as the spin Hall effect. Here we show that magnetic microscopy based on a single nitrogen-vacancy defect in diamond can provide a direct determination of the internal wall structure in ultrathin ferromagnetic films under ambient conditions. We find pure Bloch walls in Ta/CoFeB(1 nm)/MgO, while left-handed Neel walls are observed in Pt/Co(0.6 nm)/AlOx. The latter indicates the presence of a sizable interfacial Dzyaloshinskii-Moriya interaction, which has strong bearing on the feasibility of exploiting novel chiral states such as skyrmions for information technologies.

J. P. Tetienne 1 T. Hingant 1 L. J. Martinez 1 S. Rohart 2 André Thiaville 2 L Herrera Diez 3 K. Garcia 3 J. P. Adam 3 J. V. Kim 3 J. F. Roch 1 Ioan Mihai Miron 4 Gilles Gaudin 4 Laurent Vila 4 B. Ocker 5 Dafiné Ravelosona 3 V. Jacques 1
1 LAC – Laboratoire Aimé Cotton
2 LPS – Laboratoire de Physique des Solides
3 IEF – Institut d’électronique fondamentale
4 SPINTEC – SPINtronique et TEchnologie des Composants
5 Singulus technology AG

Jean-Philippe Tetienne 1, 2 Thomas Hingant 1, 2 Loïc Rondin 2 Stanislas Rohart 3 André Thiaville 3 Emilie Jué 4 Gilles Gaudin 4 Jean-François Roch 1 Vincent Jacques 1, 2
1 LAC – Laboratoire Aimé Cotton
2 LPQM – Laboratoire de Photonique Quantique et Moléculaire
3 LPS – Laboratoire de Physique des Solides
4 SPINTEC – SPINtronique et TEchnologie des Composants

François Boulogne 1 Ludovic Pauchard 2 Frédérique Giorgiutti-Dauphiné 2 Robert Botet 3 Ralf Schweins 4 Michael Sztucki 5 Joaquim Li 6 Bernard Cabane 7 Lucas Goehring 8
1 LPS – Laboratoire de Physique des Solides
2 FAST – Fluides, automatique, systèmes thermiques
3 LPS – Laboratoire de Physique des Solides d’Orsay
4 ILL – Institut Laue-Langevin
5 ESRF – European Synchrotron Radiation Facility
6 CIM2 – Laboratoire de Chimie Inorganique et Matériaux Moléculaires
7 PMMH – Physique et mécanique des milieux hétérogenes (UMR 7636)
8 MPIDS – Max Planck Institute for Dynamics and Self-Organization

Abstract : Reaction fronts evolving in a porous medium exhibit a rich dynamical behaviour. In presence of an adverse flow, experiments show that the front slows down and eventually gets pinned, displaying a particular sawtooth shape. Extensive numerical simulations of the hydrodynamic equations confirm the experimental observations. Here we propose a stylized model, predicting two possible outcomes of the experiments for large adverse flow: either the front develops a sawtooth shape, or it acquires a complicated structure with islands and overhangs. A simple criterion allows to distinguish between the two scenarios and its validity is reproduced by direct hydrodynamical simulations. Our model gives a better understanding of the transition and is relevant in a variety of domains, when the pinning regime is strong and only relies on a small number of sites.

Thomas Gueudré 1 Awadhesh Kumar Dubey 2 Laurent Talon 2 Alberto Rosso 3
1 LPTENS – Laboratoire de Physique Théorique de l’ENS [École Normale Supérieure]
2 FAST – Fluides, automatique, systèmes thermiques
3 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques

Abstract : The implications of soft ‘patchy’ interactions on the orientational disorder-order transition of strongly elongated colloidal rods and flat disks is studied within a simple Onsager-van der Waals density functional theory. The theory provides a generic framework for studying the liquid crystal phase behaviour of highly anisometric cylindrical colloids, which carry a distinct geometrical pattern of repulsive or attractive soft interactions localised on the particle surface. In this paper, we apply our theory to the case of charged rods and disks for which the local electrostatic interactions can be described by a screened-Coulomb potential. We consider infinitely thin rod-like cylinders with a uniform line charge and infinitely thin discotic cylinders with several distinctly different surface charge patterns. Irrespective of the backbone shape, the isotropic-nematic phase diagrams of charged colloids feature a generic destabilization of nematic order, a dramatic narrowing of the biphasic density region and a reentrant phenomenon upon reducing the electrostatic screening. At higher particle density the electrostatic repulsion leads to a complete suppression of nematic order in favour of spatially inhomogeneous liquid crystals.

H. H. Wensink 1 E. Trizac 2
1 LPS – Laboratoire de Physique des Solides
2 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques